A known partial surface treatment apparatus is disclosed in JP2011-219858A (which will be hereinafter referred to as Patent reference 1). The known partial surface treatment apparatus includes a first electrode member electrically connected to a treatment object which is made of metal and which includes an outer circumferential surface and a circumferential groove formed at the outer circumferential surface. The known partial surface treatment apparatus includes a second electrode member including an inner circumferential surface facing the outer circumferential surface and the circumferential groove, the inner circumferential surface being spaced apart from the outer circumferential surface and the circumferential groove along an entire circumference of the inner circumferential surface. The known partial surface treatment apparatus includes a pair of annular-shaped elastic sealing members each of which is nonconductive, the annular-shaped elastic sealing members being configured to seal, at both sides relative to the circumferential groove, a clearance formed between the outer circumferential surface and the inner circumferential surface. The known partial surface treatment apparatus includes a circumferential groove portion accommodating each of the annular-shaped elastic sealing members in such a manner that the annular-shaped elastic sealing member is spaced apart from the outer circumferential surface and that the annular-shaped elastic sealing member is movable in a diameter reduction direction. The known partial surface treatment apparatus includes a pressure applying mechanism configured to supply a pressurized fluid to an outer circumferential side of the annular-shaped elastic sealing members fitted into the circumferential groove portions in order to move the annular-shaped elastic sealing members in the diameter reduction direction, an inner circumferential side of each of the annular-shaped elastic sealing members being in pressure contact with the outer circumferential surface in a case where the annular-shaped elastic sealing members are moved in the diameter reduction direction, the pressure applying mechanism configured to release the pressure contact. The known partial surface treatment apparatus includes a supply flow passage through which electrolyte solution is supplied to a space formed between the outer circumferential surface and the inner circumferential surface, the space being sealed with the pair of annular-shaped elastic sealing members. The annular-shaped elastic sealing member of the known partial surface treatment apparatus is formed in a shape including a pair of annular-shaped side wall portions and an annular-shaped end portion. The pair of annular-shaped side wall portions are configured to be in slidably contact with groove side surfaces, which face each other, of the circumferential groove portion while the pair of annular-shaped side wall portions are apart from each other in a groove width direction. The annular-shaped end portion connects inner circumferential portions of the respective annular-shaped side wall portions to each other serially. The annular-shaped elastic sealing member of the known partial surface treatment apparatus is formed in an annular shape where the same cross-sectional shape continues along the entire circumference thereof. An inner circumferential side of the annular-shaped end portion is in pressure contact with the outer circumferential surface of the treatment object.
According to the known partial surface treatment apparatus disclosed in Patent reference 1, at the both sides relative to the circumferential groove, the annular-shaped elastic sealing members seal the clearance between the outer circumferential surface of the treatment object and the inner circumferential surface of the second electrode member. Then, the electrolyte solution is supplied to a space which is formed between the outer circumferential surface and the inner circumferential surface and is sealed with the annular-shaped elastic sealing members, and thus a surface treatment is conducted relative to the circumferential groove.
In order to seal the clearance between the outer circumferential surface and the inner circumferential surface, the pressure applying mechanism supplies pressurized fluid such as compressed air to a portion between the pair of annular-shaped side wall portions of the annular-shaped elastic sealing member fitted into the circumferential groove portion, and accordingly the annular-shaped elastic sealing member is moved in the diameter reduction direction in which the inner circumferential side of the annular-shaped end portion is in pressure contact with the outer circumferential surface. Accordingly, a circumferential length, at the inner circumferential side, of the annular-shaped end portion before sealing the clearance is longer compared to a circumferential length, at an outer circumferential side, of the treatment object with which the inner circumferential side of the annular-shaped end portion is to be in pressure contact.
According to the annular-shaped elastic sealing member provided at the known partial surface treatment apparatus, the inner circumferential sides of the pair of annular-shaped side wall portions are connected to each other at the annular-shaped end portion. The annular-shaped elastic sealing member of the known partial surface treatment apparatus is formed in the annular shape which continues in the same cross-sectional configuration along the entire circumference. As a result, in association with an elastic deformation of the annular-shaped elastic sealing member in the diameter reduction direction, wrinkle tends to be formed at the annular-shaped elastic sealing member due to a compressing force generated at the annular-shaped elastic sealing member in a circumferential direction thereof.
In a case where a large wrinkle is generated at the annular-shaped elastic sealing member sealing the clearance, the electrolyte solution supplied to the space which is formed between the outer circumferential surface and the inner circumferential surface and which is sealed with the pair of annular-shaped elastic sealing members may leak out from the wrinkled portion.
In order to avoid such a leakage at the wrinkled portion, it can be conceived that a moving speed of the annular-shaped elastic sealing member in the diameter reduction direction is reduced so that small wrinkles are generated in a spread-out manner in the circumferential direction of the annular-shaped elastic sealing member, for example. However, in a case where the annular-shaped elastic sealing member is elastically deformed over a long period of time, the surface treatment may not be performed efficiently.
In addition, in a case where the electrolyte solution leaks out towards the outer circumferential side of the annular-shaped elastic sealing member via the wrinkled portion, the leaking electrolyte solution is mixed with the pressurized fluid supplied to the outer circumferential side of the annular-shaped elastic sealing member. As a result, inconvenience tends to occur, for example, the pressure applying mechanism and/or an electrolyte solution distribution mechanism may be damaged.
A need thus exists for a partial surface treatment apparatus which is not susceptible to the drawback mentioned above.